There is an increasing need for low toxicity, low flammability liquid hydrogen gettering agent that can be used, for example, to help fiber optic cables survive the harsh environment encountered in down-hole fiber optic sensing applications. Such fiber optic cable is used, for example, to interconnect a down-hole fiber optic sensor with instrumentation located at the surface of a well bore.
Down-hole environmental conditions typically include high temperatures and high partial pressures of hydrogen. Both molecular (H2) and atomic (H) hydrogen from various sources, such as environmental hydrogen sulfide (H2S) and the corrosion of metallic components, may be present in the down-hole environment. It is well known that hydrogen permeation into optical fibers can significantly decrease the power of light transmitted through the fibers. Therefore, the fibers in these cables are typically protected from hydrogen by various combinations of hydrogen barriers (such as gold, aluminum or copper layers) and hydrogen gettering agents.
Typically, these gettering agents are metallic (Y, Pd, Zr) or metal catalyzed unsaturated organic molecules that are dissolved or suspended in a petroleum or synthetic gel. These gettering gels are typically deployed within the inner diameter of an inner cable sheath, in intimate contact with the optical fibers. The function of these agents is to scavenge any hydrogen passing through the hydrogen barrier layer(s). Liquid gels are typically preferred to solids because they are easier to deploy within a cable. A shortcoming associated with existing gettering gels is their limited stability and H2 scavenging density. A common gettering gel, sold under the trade name Sepigel (available from Seppic Corp. of Fairfield, N.J.), for example, will scavenge roughly three cubic centimeters (cc) of H2 per gram at standard temperature and pressure, or 0.1348 grams-mole per kilogram (g-mole/kg). This is insufficient for high-density hydrogen exposure in some down-hole environments. Though the composition of Sepigel is a trade secret, typical unsaturated organic compounds found in gettering gels require a catalyst to promote appreciable hydrogenation, making it more complicated and more costly to manufacture a suitable agent, and making it hard to achieve high stability, low toxicity, and low flammability.
Thus, there is a need for an improved hydrogen gettering gel for use with down-hole optical fiber cables and similar applications.